The best doctors answer our questions honestly, including telling us when they don't really know the answer. Life expectancy is one of those cases. They know what the statistics say for a group of patients, but those numbers may not apply to one individual patient. Some people beat the odds and some people don't. Perhaps it's better that we don't know which group we're in; that's what gives us each the hope and determination to succeed.
Make sure your mom knows that nobody knows for certain how long she'll live. If you believed the statistics in 1996, my wife had a 2-year life expectancy at the time, but she's going to be at the
Survivors Celebration in Phoenix this weekend. We've lost too many people to these diseases but we repeatedly hear from people who are still here despite dire predictions that they wouldn't make it this far.
I can understand why you are nervous, but from what you've said I think your mom is ready to hear the facts and is prepared to cope with them.